The present embodiments relate to an apparatus and method for determining a distance.
The determination of position information of objects of variable position plays an important role in wide areas of technology. Perhaps the simplest method for determining the position of an object is to dispose a transmitter on the object, the position of the transmitter being located on the basis of transmitted signals. There are also measuring methods, for example, which operate on the basis of a measuring device for measuring a distance in a contactless manner with the aid of an infrared detector or an ultrasonic detector. However, the application of such solutions is not favorable in many areas, as such solutions are associated with too high an outlay. Also, these methods are associated with measures that are disadvantageous with respect to the object the position of which is to be determined (e.g., the radiation emitted by a transmitter used for position determination may be undesirable).
One example of a technical apparatus that requires position determination that is subject to certain basic conditions is the determination of the position of leaves of a multileaf collimator in medical engineering. Multileaf collimators are generally used in radiation devices for tumor therapy. The multileaf collimator is used to narrow down the beam profile of the radiation device so that the body region to be irradiated is encompassed by the therapy beam in a manner that corresponds as closely as possible to the form of the body region. To tailor the form of the beam profile to the region to be irradiated, collimators generally consist of individual, thin (e.g., 2 to 4 mm thick) leaves made of a material with a high absorption capacity for x-ray and gamma radiation. The leaves are disposed parallel to the radiation direction and can be displaced independently of one another in a plane perpendicular to the radiation direction. Each leaf is supported in a fixed guideway and provided with a corresponding actuator.
It must be possible for the position of each leaf to be measured independently of the actuator at short time intervals compared with the radiation period in order to be able to check the correspondence of the leaf positions to treatment requirements. It would be complex and possibly disruptive to position sensors or other measuring apparatuses, and in some instances, associated cable connections, on the movable leaves.
A method for determining the position of leaves in a multileaf collimator is specified, for example, in US 2006/0072849 A1. It is proposed here to use the projection of light emitted onto the multileaf collimator for position determination purposes. This procedure uses an additional light source and is comparatively complex with respect to the conversion of the light projection to quantitative information, which can be used, for example, to control the actuators of the collimator.
In US 2009/0010395 A1, it is proposed to carry out position determination for a multileaf collimator using a camera, which records the multileaf collimator. The recorded image is then used to determine position information. This solution requires an additional camera and is likewise complex with respect to the conversion of the recorded image to position information for the individual leaves of a multileaf collimator.